Specification is ongoing in 3GPP (Third Generation Partnership Project) for E-UTRAN (Evolved Universal Terrestrial Radio Access Network) that is one of the next generation of radio access networks. Another name used for E-UTRAN is the Long Term Evolution (LTE) Radio Access Network (RAN). A base station in this concept is referred to as an eNB (E-UTRAN NodeB). Base stations, such as eNBs, normally provide radio access network services to relatively many user equipments.
The studies also include the possibility to have base station functionalities for home or small area coverage for a limited number of users. This type base station is referred to as a HNB (HomeNodeB) or FBS (femto base station). The FBS provides normal coverage for the end users within the small area and are connected to the mobile core network using readily available internet connectivity. The coverage provided by the FBS is called a femto cell, also known as a Closed Subscriber Group (CSG) cell in 3GPP.
One motivation behind the femto cell movement is to provide cheaper call or transaction rates/charges when connected via the FBS (femto cell) compared to when connected via the eNB (macro cell). Another motivation is to provide improved indoor coverage while off-loading traffic from relatively expensive macro radio access networks to relatively inexpensive public Internet. The FBS would in most instances use the end users already existing broadband connection (e.g. xDSL, Cable) to achieve connectivity to the operators mobile core network and possibly to other eNB/FBS.
Unlike the current radio access networks in which operators integrate relatively few (hundreds) high-capacity radio base stations connected over relatively secure private networks to Radio Network Controllers (RNCs), access via femto cells is likely to require the operators to integrate relatively many (hundreds of thousands or more) low-capacity FBSs connected over relatively insecure/untrusted public Internet. Complicating the matter is that the FBSs can be moved, added or changed at any time. The femto cell idea promises many benefits, but also presents many challenges including challenges to access control.